Seasonal variation in blood pressure is modulated by gender and age but not by BMI in a large Taiwanese population, 1996-2006.

Previous research has found that blood pressure tends to be higher in winter and lower in summer. The present study examined seasonal variation in blood pressure by gender, hypertension medication, age group, and body mass index using contemporary Taiwanese data. Over 400,000 health screening records collected biennially between 1996 and 2006 were used to calculate average monthly systolic (SBP) and diastolic blood pressure (DBP) measurements. Generalized estimating equations were used to estimate the difference between the highest and lowest mean monthly blood pressure measurements. Mean monthly blood pressure measurements were higher in winter than in summer for all age groups, regardless of medication for hypertension. The largest difference in mean monthly blood pressure between summer and winter months was 5.3 mm Hg (Standard error = 0.7) for SBP and 3.2 mm Hg (Standard error = 0.7) for DBP. These differences were more pronounced: in SBP than in DBP; in men than in women; and in older than in younger participants. Body mass index was not clearly associated with seasonal variation in blood pressure. Seasonal variation in blood pressure among contemporary Taiwanese populations is modest and may only approach clinical significance for the diagnosis and treatment of hypertension and the prevention of cardiovascular disease amongst older male individuals.